Inter-server dynamic transfer method for virtual file servers

ABSTRACT

An object of the present invention is to dynamically transfer a virtual file server within a cluster that is configured by a plurality of file servers in which virtual file servers are set up. A storage system includes: a first file server; a second file server; and a disk subsystem, in which: the first file server and the second file server each include a virtual file server control unit that sets up the virtual file server; the virtual file server includes a routing table that stores path information necessary for communication; and the virtual file server started up in the second file server determines a communication path by using the routing table used by the virtual file server in the first file server after taking a failover from the virtual file server of the first file server to the second file server.

This is a continuation application of U.S. Ser. No. 10/860,319, filedJun. 4, 2004.

CLAIM OF PRIORITY

The present application claims priority from Japanese applicationP2004-79882 filed on Mar. 19, 2004, the content of which is herebyincorporated by reference into this application.

BACKGROUND

The present invention relates to a storage system in which a cluster isconfigured by a plurality of file servers in which virtual file serversare set up. In particular, the present invention relates to a virtualfile server taking over technique.

In a logical partition technique of a computer, resources within thecomputer such as a processor and memory are logically divided, and eachallocated to a virtual computer.

A technique has been proposed for setting up virtual file servers, whichare virtual service units operating on one file server, with each of thevirtual file servers residing on different networks. This is achieved byapplying the logical division technique and dividing network resourcesor the like for each virtual file server. According to the technique forsetting up virtual file servers, it becomes possible to provide separateservices for a plurality of network segments that possess the sameprivate address by using one file server (refer to US 2003/0135578 A,for example).

Further, a failover function is known in which plural file serversmonitor one another by periodically reporting operation status amongthem via communication path or shared disks, and one file server takesover another file server's service upon detecting the failure of theanother file server (refer to U.S. Pat. No. 6,317,844, for example).

SUMMARY

The transfer of the virtual file servers between the file servers forcases where a cluster is configured by using the plural file serversthat include the virtual file servers is not considered, however.

Further, the virtual file servers cannot be transferred between the fileservers. Accordingly, load balance in units of the virtual file serverscannot be performed, and the load may concentrate in a specific fileserver.

An object of the present invention is to dynamically transfer a virtualfile server within a cluster that is configured by a plurality of fileservers in which virtual file servers are set up.

The present invention provides a storage system comprising: a first fileserver; a second file server; and a disk subsystem, wherein: each of thefile server comprise: a network interface that inputs/outputs the dataon a network; and a virtual file server controlling unit that controlsstartup and shutdown of a virtual file server, and sets up the virtualfile server in the file server; the virtual file server comprises: anetwork processing unit that transmits and receives signals to and fromthe network by using settings of the network interface and the networkinterface; and a routing table that stores path information necessaryfor communicating with devices that are connected through the networkinterface; and the virtual file server started up in the second fileserver determines a communication path by using the routing table usedby the virtual file server in the first file server, after the virtualfile server of the second file server failover from the virtual fileserver of the first file server.

According to the present invention, by dynamically transferring virtualfile servers within a cluster that is configured by a plurality ofservers (devices) in which virtual file servers are set up, it becomespossible to perform failover for only the virtual file servers in whicha failure occurs, and it becomes possible to perform load balance inunits of the virtual file servers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing a configuration of a storage systemaccording to an embodiment of the present invention.

FIG. 2 is a functional block diagram of a storage system according to anembodiment of the present invention.

FIG. 3 is a diagram for explaining tables that are used in a storagesystem according to an embodiment of the present invention.

FIG. 4 is a diagram for explaining failover procedures in a storagesystem according to an embodiment of the present invention.

FIG. 5 is a diagram for explaining a virtual file server disposalsetting screen in a storage system according to an embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention are explained below with referenceto the drawings.

FIG. 1 is a block diagram showing a configuration of a storage systemaccording to an embodiment of the present invention.

A storage system 1 of the embodiment of the present invention comprisesa plurality of file servers 10 and 20, and a disk subsystem 40. Thestorage system 1 constitutes an NAS (network attached storage). Further,the file server 10 and the file server 20 configure a cluster.

The file server 10 is composed and configured by hardware includingnetwork interfaces 11 to 13, a CPU 14, a main memory 15, and a diskadapter 16.

Further, resources that are provided to the file server 10 (the networkinterfaces 11 to 13, the CPU 14, the main memory 15, and the diskadapter 16) configure virtual file servers 10 a, 10 b, and 10 c thatoperate independently within the file server 10 by running programs thatconfigure the virtual file servers 10 a, 10 b, and 10 c on the CPU 14.That is, the CPU 14 runs the programs that configure the virtual fileservers and that are stored in the main memory 15, so that a pluralityof virtual file servers are constructed in the file server 10, and theresources (the CPU 14, the main memory 15, the disk adapter 16, and thelike) are shared between the virtual file servers.

The network interfaces 11 to 13 are interfaces to clients (not shown),and perform communication according to a protocol such as TCP/IP. Itshould be noted that the network interfaces that can performcommunication according to fiber channels or iSCSI (internet SCSI) mayalso be used. Further, the network interfaces 11 to 13 may be connectedto a network (VLAN, Virtual LAN) according to virtual groups set upwithin the network. In addition, the network interfaces 11 to 13 areeach connected to different networks (different segments) from amongnetworks 6 a, 6 b, and 6 c.

The disk adapter 16 performs protocol processing for a disk subsystem40, such as a fiber channel.

The file server 10 can access an LU (logical unit) within the disksubsystem 40 by using the disk adapter 16, and can read and write datathat is stored in a disk drive.

It should be noted that, although the file server 10 is explained here,the file server 20 also has a similar configuration. The file server 10and the file server 20 are configured by using physically differenthardware.

The file server 10 and the file server 20 are connected by a clustercommunication path 50. The cluster communication path 50 may be acommunication path such as a LAN or an Infini-band provided within thestorage system 1, and may be made via an external network.

The file server 10 and the file server 20 mutually monitor each other'sstates by mutual communication of the states. A cluster is configured bythe file server 10 and the file server 20. It should be noted that thefile server 10 and the file server 20 can mutually observe each other'sstates by sharing a disk cache or a specific region of a disk drive andperiodically reading and writing predetermined data, without using aspecific cluster communication path.

The disk subsystem 40 is connected to the file server 10, and comprisesa disk controlling unit 41, a disk cache 42, and disk drives 44 a, 44 b,44 c, and 44 d.

The disk controlling unit 41 receives data input/output requests fromthe disk adapter 16 of the file server 10, controlling data input/outputon the disk drives 44 a, 44 b, 44 c, and 44 d.

The disk cache 42 temporarily stores data read out from the disk drives44 a, 44 b, 44 c, and 44 d, and data to be written into the disk drives44 a, 44 b, 44 c, and 44 d. The disk cache 42 improves the accessperformance of the storage system 1 with respect to clients.

The logical units (LUs), which are units that an OS can recognize as onedisk, are set up on the disk drives 44 a, 44 b, 44 c, and 44 d. Further,the logical units are configured by RAID (redundant array of independentdisks), and allow for redundancy for the stored data. Accordingly, thestored data is not lost even if a failure occurs in a portion of thedisk drive 44 a, 44 b, 44 c, or 44 d.

A management terminal 2 is a computer unit comprising a CPU, a memory, astorage unit, and a network interface. The management terminal 2operates management programs in order to perform settings and the likeon the cluster and the file servers. It should be noted that onemanagement terminal may be provided for each virtual server.

The networks 6 a, 6 b, and 6 c are networks that perform communicationby using protocols such as TCP/IP.

FIG. 2 is a functional block diagram of a storage system according to anembodiment of the present invention.

The virtual file server 10 a, the virtual file server 10 b, and thevirtual file server 10 c are set up in the file server 10. The virtualfile server 10 a is explained below. The virtual file servers 10 b and10 c also have the same configuration.

The virtual file server 10 a comprises a network processing unit 105 anda virtual file server management unit 106.

The network processing unit 105 sets up the network interfaces 11 to 13that included in the virtual file server, and transmits data and controlsignals to, and receives data and control signals from, the networks byusing the network interfaces. Further, the network processing unit 105also performs processing related to a network file system (NFS), commoninternet file system (CIFS), or the like.

The virtual file server management unit 106 makes settings (such asnetwork settings, mounting of file system, and user management) for eachof the virtual file servers based on instructions from the managementterminal 2.

Further, the virtual file server 10 a comprises a network interfaceinformation 101, a routing table 102, a mount table 103, and a devicefile 104.

Information (such as a protocol file adapted to determine acommunication protocol such as a communication transfer length) forcontrolling the accessible network interfaces 11 to 13 by the virtualfile server 10 a is included as recorded information in the networkinterface information 101.

Routing information necessary for communicating with devices that areconnected to the networks 6 a, 6 b, and 6 c through the networkinterfaces 11 to 13 is stored in the routing table 102. The routingtable 102 is provided as divided for each of the virtual file servers.Accordingly, the different virtual file servers of the same file server10 can be connected to different network segments using the same IPaddress.

File system information that is accessible by the virtual file server 10a (such as mount points and device names) is stored in the mount table103.

The device file 104 is a file for accessing the LUs. A device driverincorporated into an OS kernel is started up by accessing the devicefile 104 when there is a request for data input/output on the disksubsystem 40, thus achieving access to the LUs on the disk subsystem 40.The mount table 103 and the device file 104 are provided as divided foreach of the virtual file servers. Accordingly, startup and shutdown canbe performed on each of the virtual file servers.

The virtual file server 1 has been explained so far. The virtual fileserver 2 and the virtual file server 3 each have the same configuration.

It should be noted that, in order to divide the file system providedaccording to each of the virtual file servers, the mount table 103 andthe device file 104 are provided as divided for each virtual fileserver. However, it is not always necessary to divide the mount table103 and the device file 104 when there is no need to divide the filesystem according to each of the virtual file servers.

Further, the mount table 103, the device file 104, and the networkprocessing unit 105 are provided as divided for each of the virtual fileservers but may be provided in a common processing unit with which themount table 103, the device file 104, and the network processing unit105 are shared by the file servers for cases where different virtualfile servers are allowed to access the same LUs.

Further, a file system processing unit 111, a disk access unit 112, aninter-server failure monitoring unit 113, a virtual file servercontrolling unit 114, a virtual file server failure monitoring unit 115,an inter-server synchronizing unit 116, and a file server managementunit 117 are provided for processing that is common to the virtual fileservers 10 a, 10 b, and 10 c. Each of the units is realized by executinga program, which is stored in the main memory 15, in the CPU 14.

The file system processing unit 111 receives requests from the virtualfile servers 10 a, 10 b, and 10 c, and instructs the disk access unit112 and the like to perform file access processing.

The disk access unit 112 receives requests from the file systemprocessing unit 111 and the like, and performs data input from, and dataoutput to, the disk subsystem.

The inter-server failure monitoring unit 113 periodically monitors theoperation state of other devices (the file server 20) within thecluster. Failover is performed for cases where a failure in another fileserver is detected in order to take over the service performed by thefailed file server.

The virtual file server controlling unit 114 controls the virtual fileservers 10 a, 10 b, and 10 c. The virtual file server controlling unit114 controls startup and shutdown, definitions and deletions, allocationand deletion of resources, and the like. That is, the virtual fileserver controlling unit 114 sets up the virtual file servers in the fileserver 10.

The virtual file server failure monitoring unit 115 monitors theoperation states of the virtual file servers 10 a, 10 b, and 10 c thatare operating within the file server 10 and the file server 20, anddetects virtual file servers in which a failure occurs.

The inter-server synchronizing unit 116 controls startup and shutdowntimings of the virtual file servers, and synchronizes startup andshutdown of the virtual file servers, through communication with thefile server 10 within the cluster. This synchronization process is aimedto synchronize the virtual file servers provided in file serversdifferent in terms of hardware.

The file server management unit 117 performs file server managementbased on instructions from the management terminal 2. For example, thefile server management unit 117 manages operation of the storage system1 according to cluster settings, network (including VLAN) configurationsettings, and the like. Further, the file server management unit 117changes the settings of the virtual file servers, issues an instructionof inter-server transfer of the virtual file server, and the like. Inaddition, the file server management unit 117 instructs the virtual fileserver controlling unit 114 to perform processing when operation of thevirtual file server is directed.

The logical units (LUs) are provided in the disk subsystem 40, and theLUs are provided as divided for use by each of the virtual file servers.For example, a logical unit LU1 is accessed by a virtual file server 1,a logical unit LU2 is accessed by a virtual file server 2, and a logicalunit LU3 is accessed by a virtual file server 3.

It should be noted that, although the logical units (LUs) are providedas divided according to each of the virtual file servers in order todivide the file system for each of the virtual file servers, it is notnecessary to divide the logical units for each virtual file server ifnot required.

A system logical unit (system LU) that is shared between the fileservers is provided in the disk subsystem 40. A variety of processingprograms and data used by the virtual file servers are stored in thesystem logical unit, which is accessible from the virtual file serversof each file server. Accordingly, the system LU functions as a commonvolume.

Configuration information and service state files are stored in thesystem LU. Physical resource allocation information for each of thevirtual file servers is contained in the information. For example,information on the network interfaces 11 to 13 and allocations of thelogical units to the virtual file servers may be contained in theconfiguration information. Further, from among pieces of informationstored in the virtual file server 10 a, information on the mount table103, the routing table 102, and the device file 104 are copied andstored in the service state file. For example, information on whatservices to provide by the virtual file servers, information on diskmounting and unmounting, and information on disk access limits areincluded as recorded information in the service state file.

A method of using the common volume discussed above is a method ofsharing the configuration information and the service state. Inaddition, adaptable is a method in which information is shared betweenthe file servers, when the configuration information or the servicestate stored in memory changes, in such a manner that notification ofthe configuration information or the service state after the change issent to other file servers through the cluster communication path 50.

FIG. 3 is a diagram for explaining tables that are used by a storagesystem according to an embodiment of the present invention.

The mount table 103 is provided for each of the virtual file servers.File system IDs, inode number (inode #), parent file systems, mountpoints, parent inode number, and device names are recorded in the mounttable 103.

The file system IDs are unique codes that identify the file system. Theinode number represents a number for a root directory of the file systemas viewed from that file system. The parent file system specifies towhich file system the file system is subordinate. The mount points arelocations at which the file systems are provided, and are path names ofthe root directories of the file systems. The parent inode numberrepresents a number for a root directory of the file system when countedfrom a higher file system. That is, a file system ID fs1 is mounted inan inode number=20 of a parent directory fs0, and an inode number=200 isallocated to a root directory of the file system ID fs1. In other words,a mount point of the file system ID fs1 is the inode number=20 on thefile system ID fs0 side, and the inode number=200 on the file system IDfs1 side. The device names are names allocated to the file systems, andare used to specify the file systems.

Corresponding entries are added to the mount table 103 each time adevice (device registered in the device file) allocated to the virtualfile server 10 a is mounted. For example, entries are added to the mounttable 103 each time a file system is mounted to a virtual file server.

The mount table 103 is provided as divided for each of the virtual fileservers. The directory configuration can thus vary between the virtualfile servers by providing the mount table 103 as divided for each of thevirtual file servers. It should be noted that it is not necessary toprovide the mount table as divided for each of the virtual file serversfor cases where a directory configuration is shared between the virtualfile servers.

The device names and device IDs are recorded in the device file 104. Forthe device IDs, unique numbers are allocated in the storage systemcorresponding to the logical unit managed by the file system.

Corresponding entries are created in the device file 104 each time adevice (disk) is allocated to a virtual file server. By using a tablethat is divided for each of the virtual file servers, access from thevirtual file servers when a disk is mounted is limited to only thedevices allocated in the table. It should be noted that it is notnecessary to provide the device file as divided for each of the virtualfile servers when the device file is shared across the virtual fileservers.

The routing table 102 is used to determine a transfer path for a packetfor cases where communication is performed through a network.Destination addresses, gateways, netmasks, and network interfaces arerecorded in the routing table 102. That is, packets are transferred froma network interface eth0 for destination addresses of 192.168.1.0 to192.168.1.255. Further, packets are transferred from a network interfaceeth1 for destination addresses of 192.168.2.0 to 192.168.2.255. Forother destination addresses, packets are transferred from the networkinterface eth0 to a gateway with an address of 192.168.1.1.

The routing table 102 is provided as divided for each of the virtualfile servers. Services can be performed for different networks in eachof the virtual file servers by providing the routing table 102 asdivided for each of the virtual file servers. That is, the networkinterface 11 that performs transmission by the virtual file server isdifferent for each of the virtual file servers, and the routing table102 is different for each of the virtual file servers. Accordingly, asystem and communication can be made with a device having the sameaddress included in another network segment.

Operation of the storage system according to an embodiment of thepresent invention is explained next.

First, a file system is mounted in a virtual file server prior to theaccess to files. The virtual file server management unit 106 performsthe mounting process according to instructions from the managementterminal 2. At this point an entry corresponding to a device is createdin the mount table using the device file.

Name resolution for the file is necessary for access to the file. Whenaccessing a certain file, it is necessary to convert the file, based onthe file name, to an identifier capable of specifying the file. Forexample, the inode number is used for file identification inside thefile system. However, requests from clients are made by use of anidentifier referred to as a file handle in NFSs (network file systems).The file handle are the same as the inode number because of one to onecorrespondence.

The inode number of the parent directory and the file name are providedin name resolution process, and the inode number corresponding to thefile is obtained. The network processing unit 105 converts the parentinode number of the mount point of the parent directory to the inodenumber of the mounted file system using the mount table when the mountpoint of the file system is get over. Name resolution is performed bypassing the inode number and the file name to the file system processingunit 111.

The file is then specified by using the identifier obtained in nameresolution process, and a request for the file is issued. When thenetwork processing unit 105 receives the inode number and an access typefor performing access, the network processing unit 105 sends the inodenumber and the access type to the file system processing unit 111. Thefile system processing unit 111 sends a request to the disk access unit112 when necessary, and the disk is accessed.

The file server 10 receives a file access request from the clientthrough the network. The virtual file server is determined dependingupon which of the network interfaces 11 to 13 receives the file accessrequest. Accordingly, the file access request is sent to the networkprocessing unit 105 of the virtual file server. The file access requestis also sent to the file system processing unit 111. The file systemprocessing unit 111 makes a response by performing disk access whennecessary, to the network processing unit 105. The response is then sentto the client after referencing the routing table 102.

FIG. 4 is a diagram for explaining failover processing procedures in astorage system according to an embodiment of the present invention.

First, the virtual file server controlling unit 114 receives a failoverinstruction of the virtual file server 1. The failover instruction isissued by the virtual file server failure monitoring unit 115 when afailure occurs in the virtual file server 1 (refer to (1 a) in FIG. 4).Virtual file system failures are supposed to occur owing to failures inthe network interface 11 or the like in the virtual file server, theinability to communicate due to failures in a network connectiondestination, the inability to access the disk subsystem 40, and thelike.

Further, the failover instruction may also be issued from the managementterminal 2 for load balance. In this case, the virtual file servercontrolling unit 114 receives the failover instruction through the fileserver management unit 117 (refer to (1 b) in FIG. 4).

Next, the virtual file server controlling unit 114 issues a shutdowninstruction for the virtual file server 1 (refer to (2) in FIG. 4). Theinter-server synchronizing unit 116 then sends a failover request toanother file server (the file server 2) composing the cluster (refer to(3) in FIG. 4).

The virtual file server controlling unit 114 of the file server 2 thenreads configuration information and the service state file from thesystem LUs (refer to (4) in FIG. 4). The virtual file server controllingunit 114 then starts up the virtual file server 1 in the file server 2(refer to (5) in FIG. 4).

When the virtual file server 1 starts up, the virtual file servermanagement unit 106 of the file server 2 mounts the file system andbegins service to the client according to an instruction from thevirtual file server controlling unit 114. That is, in order to performthe same service in the file server 2 as that performed in the fileserver 1, it is necessary to take over the service state file of thevirtual file server 1 in the file server 1, which includes the mounttable 103, the device file 104, and the routing table 102, to thevirtual file server 1 starting up in the file server 2. Accordingly, thefile server 2 reads the contents of the tables stored in the system LUs.It should be noted that a configuration may also be used in which,instead of reading the configuration information and the service statefrom the system LUs of the disk subsystem 40 during failover asdescribed above, the configuration information and the service state aresent from the file server 1 to the file server 2 through the clustercommunication path 50 whenever there are changes in the configurationinformation or the service state. The file server 2 may then use theconfiguration information and the service state, which are obtained fromthe file server 1 in advance through the cluster communication path 50,during failover.

The virtual file server 1 that has started up in the file server 2 canthus perform the same work as the virtual file server 1 that operated inthe file server 1. For example, the virtual file server 1 that hasstarted up in the file server 2 uses the same routing table as thevirtual file server 1 that operated in the file server 1, and thereforethe same communication path can be defined in the same network segmentas that employed before.

It should be noted that issuing of the shutdown instruction for thevirtual file server 1 in the file server 1 may also be performed afterstarting up the virtual file server 1 in the file server 2. However, itis necessary for the inter-server synchronization unit 116 tosynchronize the operation of the file server 1 and the operation of thefile server 2 so that service by the file server 2 begins after shutdownof service by the file server 1.

FIG. 5 is a diagram for explaining a virtual file server setting screenin a storage system according to an embodiment of the present invention.

Instructions for setting up and transferring the virtual file serversare issued from the management terminal 2 through the file servermanagement unit 117. A graphical user interface (GUI) or command lineinterface (CLI) may be used as a user interface.

With the virtual file server setting screen shown in FIG. 5, which fileserver operates a virtual file server (VS#) within the cluster can beset for each virtual file server.

In the disposal setting screen, a device# represents a file server(device) configuring the cluster, and VS# represents a virtual fileserver allocated. With the screen, a user selects file servers to startup virtual file servers, and places a mark on the virtual file serversone by one. Changes are then reflected by operating an update button,and the information set is stored in the system LUs as configurationinformation. The virtual file servers then transfer dynamically.

Further, commands are set with the virtual file server and the fileserver number (device number) as variables for cases where a CLI isused, for prescribing a correspondence between the virtual file serversand the file servers. For example, a command such as “vnas alloc (name){device#:device number}” is defined.

In the embodiments of the present invention explained above, whenperforming failover of a virtual file server of the file server 10 tothe file server 20, the virtual file server controlling unit 114 of thefile server 10 reads the configuration information, a copy of the mounttable, a copy of the routing table, and a copy of the device file fromthe system LUs, and starts up a virtual file server in the file server20. A virtual file server that is the same as that of the file server 10can accordingly be started up in the file server 20. Further, by takingover the configuration information and the service state information,and by starting up and shutting down the virtual file servers withsynchronization between the file servers, the servers (devices) thatoperate the virtual file servers can be changed even during operation ofthe file servers.

In particular, a copy of the routing table is read from the system LUs,and a virtual file server starts up in the file server 20. Accordingly,the virtual file server that starts up in the file server 20 can definea communication path by using the routing table. The same communicationpath in the same network segment as that employed previously cantherefore be defined.

While the present invention has been described in detail and pictoriallyin the accompanying drawings, the present invention is not limited tosuch detail but covers various obvious modifications and equivalentarrangements, which fall within the purview of the appended claims.

1. A management terminal comprising; a CPU; a management programexecuting to perform settings on the file servers; and a networkinterface coupled to a network, to which the file servers are coupled,wherein the management program: instructs each of the file servers toconfigure plural virtual file systems, and issues a file system transferinstruction to one of the file servers, the file system transferinstruction instructs the one of the file servers to transfer a virtualfile system configured in the one of the file servers to another one ofthe file servers; wherein, according to one of the file system transferinstructions, the one of the file servers: shuts down execution of thevirtual file system, and transfers configuration of the virtual filesystem to another one of the file servers; and the another one of thefiler servers: obtains the configuration information of the virtual filesystem whose configuration is transferred, and configures the virtualfile system using the configuration information obtained, wherein eachof the file servers is coupled to a storage system including a sharedlogical unit shared between the file servers and the configurationinformation for the plural virtual file systems is stored in the sharedlogical unit, when the management program issues the file systemtransfer instruction, the configuration information indicating a logicalunit in the storage system assigned for the virtual file system and thenetwork interface used for the virtual file system is updated accordingto the file system transfer instruction, and the another one of the fileservers reads the updated configuration information from the sharedlogical unit and configures the virtual file system using theconfiguration information.
 2. A management terminal according to claim1, wherein the file system transfer instruction includes an identifierof the another one of the file servers and an identifier of the virtualfile system that is to be transferred from the one of the file serversto the another one of the file servers.
 3. A management terminalaccording to claim 2, wherein the one of the file servers, which is asource of the transfer, and the another one of the file servers, whichis a destination of the transfer, designate the virtual file system tobe transferred from the one of the file servers to the another one ofthe file servers by using the identification of the virtual file system,and the another one of the file servers obtains the configurationinformation of the designated virtual file system from the configurationinformation of plural virtual file systems.
 4. A management terminalaccording to claim 1, wherein the configuration information includes arouting information for the virtual file system, a mounting informationfor the virtual file system, and device files for the virtual filesystem.
 5. A computer system comprising: a storage system storing data,plural file servers controlling input and output of data on the storagesystem, and a management terminal managing the file servers, wherein amanagement terminal comprising: a CPU; a management program executing toperform settings on the file servers; and a network interface coupled toa network, to which the file servers are coupled, wherein the managementprogram: instructs each of the file servers to configure plural virtualfile systems, and issues a file system transfer instruction to one ofthe file servers, the file system transfer instruction instructs the oneof the file servers to transfer a virtual file system configured in theone of the file servers to another one of the file servers; wherein,according to the file system transfer instruction, the one of the fileservers: shuts down execution of the virtual file system, and transfersconfiguration of the virtual file system to the another one of the fileservers, and the another one of the file servers: obtains theconfiguration information of the virtual file system whose configurationis transferred, and configures the virtual file system using theconfiguration information obtained, wherein each of the file servers iscoupled to a storage system including a shared logical unit sharedbetween the file servers and the configuration information for theplural virtual file systems is stored in the shared logical unit, whenthe management program issues the file system transfer instruction, theconfiguration information indicating a logical unit in the storagesystem assigned for the virtual file system and the network interfaceused for the virtual file system is updated according to the file systemtransfer instruction, and the another one of the file servers reads theundated configuration information from the shared logical unit andconfigures the virtual file system using the configuration information.6. A computer system according to claim 5, wherein the file systemtransfer instruction includes an identifier of the another one of thefile servers and an identifier of the virtual file system to betransferred from the one of the file servers to the another one of thefile servers.
 7. A computer system according to claim 6, wherein the oneof the file servers, which is a source of the transfer, and the anotherone of the file servers, which is a destination of the transferdesignate the virtual file system to be transferred from the one of thefile servers to the another one of the file servers by using theidentification of the virtual file system, and the another one of thefile servers obtains the configuration information of the designatedvirtual file system from the configuration information of the pluralvirtual file systems.
 8. A computer system according to claim 5, whereinthe configuration information includes a routing information for thevirtual file system, a mounting information for the virtual file system,and device files for the virtual file system.